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bh=lYmhCndv6D6zxy0kLorHB0ixdkNzSVX/DeO0ZDxZWts=; b=So5sycRDF4rIYqkxYpgbI9Rp8GYgdiSooXN1Rvl2cqZRaxvLEw+JXalrUcamHFz7y4 LKKiTt+IQGh2B5ceROA3FoPjMef1BPurSK8TCSIauCJqotECMvTmUIGZGzYXmVaT6QEp V17vqRE29NbOfQos3O+DBleD3P/ZO0kpfteBeSaXnBMAKbWEv7kFqkl2ZrA5RbGT53xJ nXB6zqd42HBazz2je7o3/7QUzZIXBw9vrga8a9NiNy10UoWQm8riySbStwXU+1UdY8YU laRBbQquFasgVv6bk/FI1biqko/JlaC0GdzUmFvIzyfZLm5/syyRHvovdPQnVHoO3+lm vo/A== X-Gm-Message-State: AOAM530jy69d7xGjXsWm1tN4plM2ePJTAsPZqLE1GRvyjv8uEaWO22vG kjLf8tevt+HEkq44mmAWkuOKs3qQUTbxl0bf1y4= X-Google-Smtp-Source: ABdhPJzZIFeSC+BDivYn/eXHJWH7fe+C3I1QxEZnu8JWh2pMJSceYo/Jr62j5E8itu50ljXAZdqXRJLbxyaNOFNhFwM= X-Received: by 2002:a17:907:764f:: with SMTP id kj15mr11537950ejc.473.1630335928716; Mon, 30 Aug 2021 08:05:28 -0700 (PDT) MIME-Version: 1.0 References: <1630286290-43714-1-git-send-email-linyunsheng@huawei.com> <1630286290-43714-2-git-send-email-linyunsheng@huawei.com> In-Reply-To: <1630286290-43714-2-git-send-email-linyunsheng@huawei.com> From: Alexander Duyck Date: Mon, 30 Aug 2021 08:05:17 -0700 Message-ID: Subject: Re: [PATCH net-next 1/2] page_pool: support non-split page with PP_FLAG_PAGE_FRAG To: Yunsheng Lin Cc: David Miller , Jakub Kicinski , Netdev , LKML , linuxarm@openeuler.org, hawk@kernel.org, Ilias Apalodimas , Jonathan Lemon , Alexander Lobakin , Willem de Bruijn , Cong Wang , Paolo Abeni , Kevin Hao , nogikh@google.com, Marco Elver , memxor@gmail.com, Eric Dumazet , David Ahern Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sun, Aug 29, 2021 at 6:19 PM Yunsheng Lin wrote: > > Currently when PP_FLAG_PAGE_FRAG is set, the caller is not > expected to call page_pool_alloc_pages() directly because of > the PP_FLAG_PAGE_FRAG checking in __page_pool_put_page(). > > The patch removes the above checking to enable non-split page > support when PP_FLAG_PAGE_FRAG is set. > > Signed-off-by: Yunsheng Lin > --- > include/net/page_pool.h | 6 ++++++ > net/core/page_pool.c | 12 +++++++----- > 2 files changed, 13 insertions(+), 5 deletions(-) > > diff --git a/include/net/page_pool.h b/include/net/page_pool.h > index a408240..2ad0706 100644 > --- a/include/net/page_pool.h > +++ b/include/net/page_pool.h > @@ -238,6 +238,9 @@ static inline void page_pool_set_dma_addr(struct page *page, dma_addr_t addr) > > static inline void page_pool_set_frag_count(struct page *page, long nr) > { > + if (PAGE_POOL_DMA_USE_PP_FRAG_COUNT) > + return; > + > atomic_long_set(&page->pp_frag_count, nr); > } > > @@ -246,6 +249,9 @@ static inline long page_pool_atomic_sub_frag_count_return(struct page *page, > { > long ret; > > + if (PAGE_POOL_DMA_USE_PP_FRAG_COUNT) > + return 0; > + > /* As suggested by Alexander, atomic_long_read() may cover up the > * reference count errors, so avoid calling atomic_long_read() in > * the cases of freeing or draining the page_frags, where we would > diff --git a/net/core/page_pool.c b/net/core/page_pool.c > index 1a69784..ba9f14d 100644 > --- a/net/core/page_pool.c > +++ b/net/core/page_pool.c > @@ -313,11 +313,14 @@ struct page *page_pool_alloc_pages(struct page_pool *pool, gfp_t gfp) > > /* Fast-path: Get a page from cache */ > page = __page_pool_get_cached(pool); > - if (page) > - return page; > > /* Slow-path: cache empty, do real allocation */ > - page = __page_pool_alloc_pages_slow(pool, gfp); > + if (!page) > + page = __page_pool_alloc_pages_slow(pool, gfp); > + > + if (likely(page)) > + page_pool_set_frag_count(page, 1); > + > return page; > } > EXPORT_SYMBOL(page_pool_alloc_pages); > @@ -426,8 +429,7 @@ __page_pool_put_page(struct page_pool *pool, struct page *page, > unsigned int dma_sync_size, bool allow_direct) > { > /* It is not the last user for the page frag case */ > - if (pool->p.flags & PP_FLAG_PAGE_FRAG && > - page_pool_atomic_sub_frag_count_return(page, 1)) > + if (page_pool_atomic_sub_frag_count_return(page, 1)) > return NULL; Isn't this going to have a negative performance impact on page pool pages in general? Essentially you are adding an extra atomic operation for all the non-frag pages. It would work better if this was doing a check against 1 to determine if it is okay for this page to be freed here and only if the check fails then you perform the atomic sub_return.